Forced Motion of a Single Particle in Micron-sized Particle Dispersion

Abstract

The role of hydrodynamic interaction between micron-sized particles on the motion of a single magnetic probe particle, on which an external magnetic force is exerted, is studied. The motion of a probe particle in an index-matched suspension of surrounding particles is investigated using an optical microscope and image analysis technique. When inter-surface distance is smaller than the diameter of probe particle, the velocity of probe particle is reduced but rarely affected by the size of surrounding particles. The reduction of probe particle velocity is well associated with Péclet number of surrounding particles, but the degree of the suppression becomes significant below the critical inter-surface distances. The hydrodynamic interaction becomes many-body problems under the condition, and as a result, the bulk viscosity becomes larger than that under complete dispersion.